A Potential Path to Emissions-Free Fossil Energy

The National Energy Technology Laboratory's chemical looping reactor, above, is the only one of its kind in the Western Hemisphere, and is pioneering the development of a promising low-carbon technology.

The President's strategy relies on deploying the low-carbon technologies we already have as well as developing new ones. One of these emerging technologies is called "chemical looping."

While chemical looping may not be a household term just yet, it represents one promising path forward for using fossil fuels as part of a clean energy future.

At most coal fired power plants, the coal is mixed with air so that it can burn. When it burns, the chemical reaction bonds together carbon from the coal and oxygen from the air to produce carbon dioxide. It also bonds together nitrogen gas from the air with oxygen to produce nitrogen oxides, which cause acid rain and smog. Separating out the nitrogen oxides from the carbon dioxide and other pollutants in the exhaust stream is both difficult and expensive.

But if you burn coal in pure oxygen instead of air, no nitrogen oxide is formed because there is no nitrogen present. The exhaust stream is almost entirely carbon dioxide and water.

This can be accomplished in a "chemical looping" system in which the coal is mixed with a metal oxide, such as iron oxide (otherwise known as iron ore). The coal reacts with the iron oxide and produces a stream of oxygen so that the coal can combust. The leftover iron oxides, which have lost some of their oxygen, flow into a separate chamber where they mix with air, which causes them to reoxidize. The iron oxides are then "looped" back into the fuel chamber, and the cycle repeats continuously.

This type of system can use coal -- or other fossil fuels -- nearly free of emissions, and produces a pure stream of carbon dioxide that would then need to be compressed and permanently stored underground.

While chemical looping could be a low-cost approach to capturing carbon dioxide, the process is still experimental compared to other common technologies for capturing carbon dioxide. We hope that will change as our work progresses over the next few years. We are experimenting with different mixes of metal oxides that could make the process much more efficient and allow for large scale use of the technology.

Ultimately, the market will decide which technologies succeed, but our goal is to create as many viable options as we can so that our abundant fossil fuel resources can be part of a clean energy future. Chemical looping is one of many promising technologies the Energy Department will pursue over the next few years, and we look forward to seeing the results.